Living Planet Unit 2, page 1 LIVING PLANET UNIT TWO SUMMARY OF UNIT TWO MATERIAL The videotapes to watch for this unit are: Video Episode 3 - The Northern Forests Video Episode 4 - Jungle For each video episode in this unit: read the CONCEPTS section in the study guide answer the Concepts Study Questions watch the Video Episode answer the Video Study Questions OVERVIEW OF UNIT 2 LEARNING OBJECTIVES Video Episode 3 - The Northern Forests To become acquainted with: 1. characteristics of conifers 2. differences between conifers and flowering plants 3. reproductive cycle of conifers vs. flowering plants 4. layers of a typical forest 5. food chains and food webs 6. types of temperate forests 7. ecology of coniferous forests: location, climate, characteristics, life forms and adaptations 8. relationship between conifers and fungi 9. relationship between voles and owls 10. characteristics of broad-leaved deciduous trees 11. ecology of temperate deciduous broad-leaved forest: locations, characteristics, life forms and adaptations 12. effects of fire on forests Video Episode 4 - Jungle To become acquainted with: 1. nitrogen cycle 2. ecology of jungles: location, climate, characteristics, life forms and adaptations 3. the layering (stratification) of jungles 4. the kapok trees, including location, characteristics, climatic differences, life forms and adaptations 5. the canopy, including location, characteristics, climatic differences, life forms and adaptations 6. relationship between flowering trees and animals 7. the jungle floor, including location, characteristics, climatic differences, life forms and adaptations Living Planet Unit 2, page 2 CONCEPTS FOR EPISODE 3: THE NORTHERN FORESTS TREES In forest communities, trees dominate the vegetation. There are many different kinds of trees, of course, and we can look at these in several ways. One way is to look at their growth habits. For instance, some trees are deciduous and others are evergreen. Deciduous trees lose all their leaves for part of the year, usually during the winter. Evergreen trees always have leaves. They lose leaves, but only a few at a time. Another way is to look at their evolutionary relationships. In this respect, trees fall into two main groups: the conifers and the broad- leaved flowering trees. Conifers are cone-bearing trees. Their seeds develop inside cones instead of flowers. (Even though Attenborough uses the term "flower" to describe the cones, this is incorrect.) The reproductive cycle of a typical conifer, such as a pine tree, takes two years to complete. During the first year, both male and female cones are produced. The male cones are very small and are grouped together in clusters. They produce enormous amounts of pollen. The female cones are larger than the male cones, but still smaller than mature female cones. They are soft, and the eggs are located within the cone, between the scales. The male cones release their pollen, which is carried by the wind to the female cones. Since the pine relies on the wind to spread its pollen, the male cones produce abundant pollen. Most of the pollen never reaches a female cone. The wind carries it everywhere (including our noses) instead of directly and efficiently to the female cones. The male cones must make enormous amounts of pollen to be sure some of it will reach a female cone. The scales of the female cone have separated just enough to allow pollen to fall between the scales. When the wind-blown pollen reaches a female cone, the pollen grains fall between the scales and reach the ovules of the female cone, where the eggs are located. After pollination, the female cone closes up. So ends the first year. During the second year, the pollen grains eat away at the ovule tissue until they reach the eggs. Then the pollen produces sperm that fuse with the eggs to form zygotes, cells that will divide to form the embryos inside the seeds. The ovules develops into seeds, and the female cones grow and mature until they are as large as the familiar pine cones used as decorations during the winter holidays. Conifers are usually evergreens that have leaves shaped like needles. The shape and structure of the needles are adaptations for dry conditions. The long thin shape of the needles decreases the amount of surface from which water can evaporate. The leaves have a thick waterproof layer (called a rind in the videotape) that protects them from drying out. The leaves have holes through which gases enter and exit. These holes are sunken into pits, which reduces evaporation. As you will hear in the videotape, conifers often live in areas with long cold winters when water is frozen and cannot be used by the trees. So, adaptations for dry conditions, such as the structure of their leaves, help the conifers survive the winters. Most of the conifers live in regions just south of the tundra. The summers are very short there, so the growing season may be as short as 90 days. Because the conifers are evergreen, they do not need to waste time in making new leaves in the spring. Instead, their needles can start producing food right away, allowing the conifers to maximize their growth during the short summer. Living Planet Unit 2, page 3 Broad-leaved trees produce their seeds inside flowers. They are much more closely related to other flowering plants, such as daisies and roses, than to conifers. The reproductive cycle of a typical broad-leaved tree, such as an oak tree, is completed in a much shorter time than in conifers. Oak trees in the Austin area, for instance, produce flowers in the spring (March and April) and produce fruits (acorns) by September and October. Thus, broad-leaved trees can reproduce in a matter of months instead of years. Although most flowering plants use animals to transfer pollen from flower to flower, most temperate broad-leaved trees rely on the wind instead. The wind-pollinated flowers of broad- leaved trees are inconspicuous with green petals. And they produce enormous amounts of pollen, just like in the conifers, and for the same reasons. Some broad-leaved trees have large, brightly colored flowers, such as peach trees and magnolias. These trees rely on bees and other animals to transfer pollen instead of the wind. The brightly colored petals of the flowers are signals used to attract the animals. In the temperate regions of the planet where there are four distinct seasons, plants must get through the winter somehow. Here, broad-leaved trees are deciduous. As the nights get longer in autumn, biochemical changes in the tree trigger the dropping of leaves. All the recyclable parts of the leaf are removed and stored in the trunk and roots, so the green color disappears, revealing the brilliant oranges, reds, and golds of unrecyclable pigments. Eventually, the stalk that holds the leaf to the tree weakens and it separates from the tree. Why lose leaves just before winter? Water is not available during the winter months. Large amounts of water will be lost across the broad surface of the leaves. During the winter, lost water cannot be replaced by the absorption of water from the soil by the roots. So, it is better to get rid of the leaves all together. This means that every spring, deciduous trees must produce new leaves. This is only possible in areas where the summers are long enough for leaf replacement, growth and reproduction. Broad-leaved forests are thus generally restricted to areas south of approximately 45 degrees North latitude. TROPHIC RELATIONSHIPS: FOOD CHAINS AND FOOD WEBS Trophic relationships are about food. To keep it simple, plants make food by photosynthesis. Since plants produce food from carbon dioxide and water, using sunlight as an energy source, plants are called producers. Any organism that utilizes the food originally produced by a producer is called a consumer. Primary consumers eat living plants. You can also call them herbivores. Think of a cow or a deer or a rabbit or the flamingo from the Rift Valley (Unit 1). Secondary consumers eat primary consumers. Tertiary consumers eat secondary consumers. And so forth. So, what do you call a consumer who eats another consumer? You can either call them predators or carnivores. Put these together and you get a simple, straight-line relationship of "who eats whom" called a food chain: grass ¼ mouse ¼ snake ¼ hawk producer ¼ primary ¼ secondary ¼ tertiary consumer consumer consumer Living Planet Unit 2, page 4 Are all trophic relationships this simple? Well, by now, your answer should be "no way." What do you do with the hawk that eats the snake but will also gladly take a nice juicy mousie for lunch? How do they fit into a food chain? grass --> mouse --> snake  Á hawk This is no longer a simple food chain, since it is not a straight-line relationship. This is the start of a food web, which maps out more complex eating relationships. Now, let's add a new type of trophic relationship. What do you call a consumer that eats both plant material and other consumers? They are called omnivores (omni = all, vore = eater). fox À ¿ grass and berries --> mouse --> snake  Á hawk What about an organism that eats dead plant and animal material? If the organism is eating recently killed animals, they are called scavengers. Scavengers include vultures eating road kill, lions that steal a recently killed antelope from cheetahs or gulls that harass pelicans until they drop the fish from their bill pouches. So, remember what we said earlier about relationships not always fitting into our categories? Look at the lion. You know from numerous TV programs that lions are predators. However, no self-respecting lion would pass up a free meal.